There are known cables having a plurality of equally spaced apart radial elements secured thereto, which act as apparatus for conveying materials behaving substantially as fluids through ducts, in which the cable slides through a tube.
The cables normally used are of the metal wire type and consequently have a relatively discontinuous surface, due to the fact that they are formed by twisting the strands together. Disks, or similar conveying elements, are molded from plastic onto the cable and are therefore relatively firmly secured, especially if they have a relatively wide base, so as to cover a reasonably long section of the cable. However, the sudden change in the rigidity of the cable, caused by the present of the disk, gives rise to problems in the case of cable paths with a large number of curves or with curves having a relatively small radius, as is often necessary in complex systems.
Due to the intrinsic relative rigidity of metal wire cables it is, in fact, necessary for the curves in the system to be made with a relatively wide radius in order to avoid excessive bending stress.
In cable conveying system it would sometimes also be desirable to use radial elements which are asymmetrical or off center with respect to the cable. This requirement however conflicts with the torsional resistance of the metal cable, which prevents the elements secured to it from moving along the path according to the curves and the positions of the return pulleys.
All this makes it highly desirable to use textile cables made of high-strength materials, such as those made available by current technologies. Their flexibility, flexural and tensile strength and tendency to accept axial torsion prove, in fact, to be highly satisfactory.
However, the relatively continuous surface of these cables makes the problem of firmly securing the disks, or the like, to the cable extremely difficult.
Moreover, cables made of textile fiber tend to become frayed when their surface threads snap as a result of mechanical stress and especially wear. This problem can be eliminated by using a continuous sheath of flexible material, with high abrasion resistance, which surrounds the cable and also protects it from becoming impregnated with the conveyed material. The use of a sheathed cable makes it practically impossible to firmly secure the disks molded onto it, or secured to it by conventional methods, with the result that up till now it has not been possible to currently and satisfactorily use these cables in conveying systems, despite the fact that their mechananical properties can be considered to be ideal for this use, especially in terms of smoothness and durability.
In the known technique, various possible solutions have been proposed for securing the radial elements to the cable, such as for example the one described in the Italian patent application No. 20245 A/84 on behalf of the same Applicant.
The known coupling means made to date however are still unsatisfactory since they are either unreliable or excessively complicated and therefore expensive to make, especially in view of the usually considerable length of the cable and of the large number of conveying elements secured to it and, moreover, the need to avoid introducing causes which could lead to fraying and snapping of the cable.
The general scope of this invention is to obviate the aforementioned problems by providing a cable, in particular for a system of the type described above, in which the conveying elements can be reliably, inexpensively and rapidly secured to any type of cable whatsoever, especially cables made of textile fiber and sheathed.